using the building gadget to place structure voids (for the intents of creating custom structures) is really useful, however you cannot see where they are being placed. It would be nice if they showed up.

As a more general solution for this, an option to highlight all blocks being placed would kinda be cool, would be useful for things like partial blocks as well such as slabs, pressure plates, etc. Like give each block in the placement preview a semi-transparent blue box thats a full block or something. And red if you run out of materials.